Antenna system



E. BRUCE ANTENNA SYSTEM May 23, 1933.

Filed March 9, 1927 5 Sheets-Sheet 1 MMI/f 6 May 23, 1933. E BRUCE1,910,147

ANTENNA SYSTEM May 23, 1933. E, BRUCE I f 1,910,147

ANTENNA SYSTEM Filed March 9, 1927 3 Sheets-Sheet 5 fFFfc/s/f I VOL Z465PHASE Q CFI Patented May 23, 1933 UNITED STATES PATH Q'P'FICE' nnMoNnBRUCE, or nun BANK, New JERSEY, AssieNoa To BELL TELEPHONE LABoc:

BA'roBIEs, INcoBBoBAr-nn, or New YoBK, N. Y., acci-recitation or NEWYonx ANTENNA SYSTEM Application :tiled March 9, 1927, Serial No.173,833, and in Great Britain January 10, 1927. A y? This inventionrelates to wave transmission, and especially to antennae adapted forshort wave radio communication.

When an ordinary electromagnetic wave traveling along the surface of theearth and having its front in a vertical plane impinges upon a verticalreceiving antenna, absorption of energy from the wave takes place inwell known manner resulting in a current in the antenna. lf severalsuoli independent antennae are spaced apart a distance of oneehalf wavelength in the direction of propagation, upwardly directed currents areset up in the first, third, etc. of these antennae at the same time thatdownwardly directed currents are set up in the second7 fourth, etc. Byconnect ing these antennae electrically so that the effects of all thesecurrents are 'added with respect to the receiving device, the responseobtained is much greater than with a single antenna. Antenna arrays ofthis type have been suggested in the past. In accordance with thisinvention an improved antenna array of .this general type suitableeither for receiving or transmitting is provided.

One fundamental aspect of the invention Vlies in connecting the verticalantennae by means of conductors in such manner that phases are takeninto account throughout the system with resulting increase ineiiiciency. This aspect of the invention may be better understood byconsidering a simple receiving antenna array comprising verticalsconnected lin series by horizontally connected wires. The arrangementmaybe such, in accordance with this invention, that a current pulse setup by the space wave inthe uppermost elemental section of the firstvertical wire, for example, is just one wave length of the wire from thelowermost elemental section of the second vertical, so that there willbe an add ino" of the current in the verticals in phase. In a simplecase the verticale are one-half wave length high and one-half wavelength apart. This additive effect may be obtained in other forms ofantennae of this general type by having corresponding elemental sectionssomewhat differently spaced as will be hereinafter described.

Tn another aspect the invention pertains to the choice of antennaheight, the preferred form of antenna being one in which the height isone-half wave length. l f 1 Another aspect of the invention relates t0the proper impedance termination of the an? C65 tenna array to obtain adesireddirectional effect by preventing undesired reflections.

fr-ain, the invention provides an antenna array of the type mentionedabove, but fo-ld- 'p ed back upon itself, so'as in general to obtain icompactness, and, in certainicases, the elimination of grounds. y

Figs. 1, 3, 5, 6 and 7 of the 'drawings show five different systems ofthe type described above; Figs. 2A, 2B, 4A and 4B are diagrams forfacilitating explanation of the invention; and Fig. 8 shows the polardirectional characteristics of the 'system of Fig. 7 In Fig. l thesinusoid shows the space distribution of the electric or the magnetic t70 ield strength of an advancing electromagnetic wave at a given'instant of time t. "The heavy yvertical and horizontal lines represent aseries of vertical orupright inductor wires r I u a half wave-lengthhigh and spaced by a half wave-length and horizontal wires f of thatlength connecting `the vertical wires. The wires are all in a kplaneperpendicular to the/wave front, and the electric field of the oncomingwave is parallel 'to the vertical f3 wires. Thus, the electromagneticwave may be such as would be sent 'from a vertical transmitting antennawire. The arrows on the conductors show the direction of current flow atthe given time t. Interconnecting the inductors or verticale u byconductors j", as shown, securesthe benefit of the cumulative effect ofthe verticals. This system satisfies cach of two conditions which it isdesirableK to fulfill, namely that the'height L be of90 proper value toproduce the optimum effective induced voltage in each of the verticals,and that the height h and the spacing of the verticals in the directionof the wave motion, and the length of the horizontal wires f have valuessuch that the resultant currents, one of which is produced'by eachvertical, are directly in phase at any point in the line so that thecumulative effect just mentioned is a maximum. (For the present it isassumed that the current Wave velocity in the Wire is equal to the spaceWave velocity in the surrounding medium.)

To show that the first condition is satisfied, reference may be had toFigs. 2A and 2B. Fig. 2Arepresents a lossless Wire u divided into smallelements 1, 2, 3, etc.,each having the same induced voltage in timephase With each other. Acurrent pulse from, say, element 3 travelstoward point P With the speed of light. By the time it reaches P, itlags behind the instantaneous induced voltage in time phase an amountdepending on the distance traveled. Fig. 2B shows the vector addition ofthese current pulses originating in elements 1, 2, 3, etc. which, for alossless line, traces along the circumference of a circle. The resultantcurrent IP Will be a maximum when it is the diameter of the circle.Since the diameter interconnects tivo elementary currents 180O outvofphase, the optimum line length must necessarily be one-half Wavelength.vFor any point other than P, the reasoning is similar. The onlydifference will be that the resultantcurrentvvill have a different phaserelation to the reference axis in the same manner as the ordinary spacephase distribution of a Wave. Thusitis seen that the arrangement in Fig.1 satisfies the first condition stated above.

Fortunately, this arrangement also satisfies the second condition (withseparation of verticals u equal to half of the wave-length because-anyelemental length in one vertical has a corresponding elementary length,in the next vertical, just one Wire Wave-length away, as illustrated inFig. 1 by a and al, likewise I) and b1. The elemental lengths a and alare here referred to as corresponding elemental lengths because, o r inthe sense that, they are the same distance from the entrance ends oftheir respective verticals I at any given instant, or in other Words thesame distance from those ends of their respective verticals which ateach instant are given equal potentials relative to the other ends bythe action of portions of the space Wave one-half Wavelength apart.

The far ends of the line or antenna may be free, as shown.V However, ifdesired, an antenna With its ends grounded as about to be described maybe employed. Preferably, when the ends are free the total length of theantenna is an integral odd multiple of half of a Wire Wave length andwhen the ends are groimded the total length of the antenna is anintegral even multiple Vof half of a Wire Wave length. By fulfillingthese conditions it is possible to obtain maximum reflection at the endsof the system and to cause the first or primary reflection of theresultant current due to the electromotive force induced in any verticalinductor a in Fig. 1, to be in phase with resultant current by thedirect propagation, due to the electromotive force induced in thatvertical inductor u, at any point in the antenna, as for example at theload 10. The condition of free termination is the practical equivalentof a change of half a Wave length, as compared with a condition ofgrounded termination, on account of the reversal of phase on refiection.Therefore, when an antenna With grounded ends is desired, switches S,which are located at the midpoints -of horizontal conductors f, may beclosed downward. Four of the verticals u are then effective.

If a line such as that in Fig. 1 were a lossless line, with noV energyextracted from it (that is, With no load connected to it) it woulddevelop a series of standing Wave sections, each being one WireWave-length in length and each functioning irrespective of the adjoiningsections. The instant a load is inserted in the line as at 10, the linecurrent amplitudes decrease and all sections feed in energy toward thisload in order to reestablish equilibrium.

In the system of Fig. 1, it is desirable to employ a character of loadand to insert the load at'a point in the line such that a maximum outputvoltage Will be developed. The load is preferably connected at themidpoint of one of the half Wave-length horizontal Wires f, at thecenter of the Wave collector, as shown in Fig. 1. The impedance whichthe load presents to the Wave collector should be as high as possibleand therefore may Well be an anti-resonant circuit, as shown at 10,tuned to the Wave length A. The anti-resonant circuit is coupled to aradio receiver (or transmitter) 11 by a resonant circuit 12.

Regarding the directional characteristics of the system of Fig. 1, thesystem is bi-directional and the outputs due to signal field strengthsin the broadside directions directions perpendicular to the plane of theantennae), are negligible.

The discussion so far has been under the assumption that the line phasevelocity is equal to the velocity of light. In long line experience,this has been found decidedly not to be the case. In fact, the line Wavevelocity is less than the space Wave velocity to suchan extent thatshould the dimensions given above be maintained, additional sectionswould not add materially to the output. In order to avoid thislimitation, should the Wire velocity be retarded, the spacing of theverticals should still be maintained at one-half a space Wave-length butthe verticals should be shortened in length sufficiently to reestablishthe proper space relation between the Wire and the space Waves. Thesystem of Fig. 1 can be extended indefinitely, to include nomics of theproblem. However, such an antenna is preferably built for a definitefrequency and a definite direction of reception, for use in point topoint communication, for example. The output voltage maximum of one ormore verticale of an antenna of this type, if the antenna were lossless,would be directly proportional to the wave length for which it wasdesigned.

It has beenstated above that the antenna system of Fig. 1 isbi-directional, meaning that it responds readily to waves from eitherhorizontal direction in the plane of the antenna. The system of Fig. 1is equally responsive tor these two opposite directions. One way inwhich asymmetry, or lack of equality, of responsiveness for the twodirections may be obtained is by rearranging the spacing of the'wiresofA half wave-length` height, while maintaining the alternate ones ofthose wires at a. wave length apart and maintaining the lengths of thehorizontal connecting wires equal to the distances between the verticalewhich they connect. Vhen the spacing of the wires u of half wavelengthheight is, by way of example, alternately a quarter and three quartersof the wave-length, as shown in Fig. 3, the antenna is responsive towaves from only one of the two opposite horizontal directions in itsplane, provided the reflections from the far end are absorbed byproperly terminating that end as shown at 15 in Fig. 3. An antennahaving this directional property will be referred to in thisspecification as a unidirectional antenna. The action i of the propertermination can be explained by reference to Figs. 4A and 4B, each ofwhich represents a single section. In Figs. 3, A and 4B, horizontalquart-er wave-length conductors f or three-.quarter wave-lengthconductors f connect adjacent verticals.

It can be shown that, in Figs. A and 4B, the resultant effective voltageinduced in a vertical u, can be represented by a lumped voltagecentrally located in that vertical, as at @l and e2. A vector picture ofthe currents and voltages for each vertical is drawn below the vertical.It is seen that the voltages phase difference between verticals is aquarter period. Assuming the velocity of the current pulses as the speedof light, one complete period elapses for a current pulse to traveldirectly from el to receiver R, likewise a quarter period is necessarybetween e2 and R. For the current pulses arriving at R via the far endreflection, e1 to R requires effectively two complete periods while e2to R requires two and three-quarter periods. Figs. 4A and 4B representreceiving conditions for waves in opposite directions. Examination ofthe current vectors, drawn below these ligures, shows receiverdirectional discrimination Jfor the direct and reflected propagationsseparately, but if both are allowed to exist simultaneously, the'directional discrimination is destroyed. Therefore, for vcompletesuppression of reception fromI one horizontal direction in the plane ofthe antenna, far end damping should be employed, as shown at 15 thephase requirements for arithmetical cur-I rent addition. Thoserequirements will also be satisfied it corresponding elements ofadjacent sections are any integral multiple of one space wave length andany integral multiple of one wire wave length apart.

A multiple section antenna such as that in Fig. 3 may be folded backupon itself and the terminating impedances connected between wires, asshown in Fig. 6, thus eliminating the necessity of ground connections.`

1n the system of Fig. 6 the two sections per se are similar to thesection disclosed in Fig. 5 and, singly, would each have theunidirectional characteristics of the section of that iigure sincetheyare similarly associated with the corresponding surge impedance andreceiver. These sections are-'so related to each other that theircurrents act cumulatively since.A although the corresponding elementsotadjacent sections are differently spaced L1 tive unidirectionalarrangement, theV wire wave length spacing is correspondingly less andsuch as to provide adequate compensation. Fig. 7 illustrates how thisscheme may be enlarged. The theoretical vpolar directionalcharacteristics-tor the antenna system of Fig. 7 are given inFig. 8. Thesymbol e in Fig. 8 represents field strength. The origin of polarcoordinates is at the tip of the right-hand arrow in Fig. 8. In Figs. 6and 7, as in the case of Figs. 3 and 5, the antenna lies in a planecontaining the direction of theelectric force in the wave front- 'of the.wave to be received (or transmitted) and peints from the receiver ingwave.

rlhe surge impedance of a lossless line, and therefore the properterminating impedance toward the oncom- Vfor such a line, isapureresistance. At the high frequencies for which these antennae areespecially well adapted, it is diiiicult to construct resistanceswithout reactive effects. An arrangement which proved most satisfactoryfor the far end line termination l5 consisted of an anti-resonantcircuit in parallel with a limiting resistance element or resistanceelement for limiting the resistance of the termination as a whole. Eventhough react-ance 1s present in the resistance element,

there exists an adjustment of the anti-resoman in Fig. 3, whichillustrates an alterna-` 100 nant circuit, which will make thecombination effectively a pure resistance. In practical antennae, wherelosses are present, the theoretical Asurge impedance contains a smallre- V12, respectively, of Fig. 1 but adjusted to simulate the impedancel5.

rIlhe electrical lengths or` wire wave lengths of the elements 10,10and-15 are substantially zero or negligibly small. In Figs. 3 and 5 theelectrical lengths ofthe conductors connecting elements 10 and l5between a onehalf wave length vertical conductor u and earth aresubstantially zero or negligibly small. In Figs. 6 and 7 the elements l5and l0 are connected at the center of one-half Wave length horizontalconductors f2 which connect the lower ends of two of the onehalf wavelength vertical wires u. In Figs. 5, 6 and 7, as in Figs. 3, 4A and 4B,conductors f and f are horizontal one-quarter wave length andthree-quarter wave length conductors respectively, each connecting twovertical wires u.

Although it wasmentioned above, it may be again pointed out that, shouldthe wire velocityV be retarded by losses, the proper phase relation withthe space wave may be reestablished by slightly shortening the length ofthe verticals.

f Fig. 8 is the calculated polar directional characteristic for theantenna system of Fig.

v7, the system being unidirectional, with maximum efectiveness for onehorizontal direction in the plane of the antenna and zero effectivenessfor the opposite direction.

Although, in the specific systems described above, the wires u arevertical and the wires f, f and f horizontal, the principle of theinvention is independent cf the absolute direction of the wires u and f,f and f. In the several specilic embodiments of the invention shown inthe drawings the wires u, it will be noted, are parallel to thedirection of the electric force in the wave front, or in other words.are parallel to the axis of polarization of the waves to be received by,or radiated from, the antenna, and the wires f, f and f areperpendicular to the axis of polarization. The term height as used inthis specification and in the claims is not restricted to verticaldimensions.

The expression integral multiple7 of a quantity, as used in thisspecification and in the claims, includes unity as the multiplierinvolved. Thus the quantity may be an integral multiple of itself.

The'dimensions mentioned above for the length, spacing, height, etc. ofthe component parts of the antenna may be increased by any integralmultiple of one wave length, since the phase relations of the voltagesand currents in the system will not be thereby altered.

In referring herein to directions in which portions of the antennaextend, difference of sign or sense is not regarded as a dierence ofdirection, although in referring to the directional characteristics ofthe antenna opposite signs or senses of direction are regarded asopposite directions.

What is claimedis:

l. An antenna for space wave communication, comprising inductors spacedin a direction of propagation of the space waves past said antenna, andcurrent conducting means connecting said inductors, the electricallength of said antenna between corresponding elementary lengths of anytwo of said inductors differing an odd integral multiple of a half wavelength from the spacing, measured in space wave lengths, of the twoinductors in said direction, at the frequency of said waves.

- 2. In combination, an antenna for space wave communication, andterminal apparatus for said antenna, said antenna comprising portionsspaced in a direction of propagation of the space Waves past saidantenna, and current paths connecting said portions" in series with eachother and said terminal apparatus, the difference between the electricallengths of said antenna betwen corresponding elementary lengths ofadjacent ones of said portions on the lone hand and said terminalapparatus on the other hand,

differing by an integral odd multiple ofi half a wave length from thespacing, measured in space wave lengths, of the adjacent portions, atthe frequency of the waves.

3. An antenna comprising a plurality of elements extending in tworight-angularly related directions, occupying a common plane,jand seriesconnected in zig-zag form and therefore comprising in part a series ofparallel non-colinear elements, the spacing of said parallel elementsbeing so related to the electrical length of a cyclically repeated unitof the antenna as a whole that, with respect to any two points separatedby such a unit length, the phase difference between currents inducedfrom a space wave Whose front is parallel with said parallel elementwill be the same as the corresponding phase dilference between currentsat the same point resulting from propagation of a Wave along the antennabetween such points.

4. In combination, an antenna for radio wave communication, comprising aconductor having a height approximately an odd integral multiple of halfof the wave length,

Vin said conductor, of current of the frequen- SLO cy of thecommunication wave, signaling apparatus, and means coupling saidapparatus to said antenna and presenting a high impedance to currentiowing in said antenna.

5. An antenna comprising a plurality of sections, each sectioncomprising two conductors and a third conductor positioned at rightangles to said two conductors and connecting said two conductors inseries, said two conductors being spaced a quarter space Wave lengthapart, and another conductor connecting two of said sections in series,the electrical lengths of said two conductors of each section and saidlast mentioned conductor being such that the time required for currentto iow from the electrical center of one of said two conductors of oneof said two sect-ions to the electrical center of the corresponding oneof said two conductors of the other section is such that at said centerpoints said current is in the same phase relation to the space waveidentified with the current.

6. An antenna system for radio wave communication, comprising conductorseach having a height approximately half of the wave length of thecommunication wave, and connecting conductors, at right angles to saidfirst conductors, joining said first conductors in series, the spacingof said iirst conductors being alternately a quarter wave length andthree quarters of a wave length.

7. An antenna comprising conductors extending in a given direction, andmeans in a plane at right angles to said conductors connecting saidconductors in series, said conductors being so spaced apart, and thelength of said antenna between corresponding elementary lengths of saidconductors being such that direct propagations in said conductorsidentified with a space wave moving in a given direction are cumulativeat a given point in said antenna, and direct propagations in saidconductors identiied with a space Wave moving in another direction aredifferential at said point.

8. An antenna system having an asymmetrical directional characteristic,comprising a plurality of antenna members connected by conductors havingsubstantially no antenna characteristics, and means terminating theantenna system in an impedance equal to the surge impedance of suchsystem.

9. In combination, an antenna system, comprising a plurality of antennamembers connected by conductors having substantially no antennacharacteristics, in which direct and reliected propagations identifiedwith a space wave moving in a given direction are cumulative anddierential, respectively, at a point in said antenna, and direct andreiiected propagations identified with a space wave moving in anotherdirection are differential and cumulative, respectively, at said point,and means rendering said reflected propagations substantially zero.

10. An antenna comprising a plurality of main conductors, eachapproximately onehalf wave length in height, and auxiliary conductorspositioned vat right angles to and connecting said main conductors inseries, said main conductors being so spaced that the successivespacings are unequal and that at the center points of alternate main'conductors the current is in the same space relation to the space waveidentified with the current.

11. An antenna accordingrto the next preceding claim and an electricalnetwork of impedance substantially equal to the surge impedance of theantenna connected between one end thereof and ground.

12. An antenna'for radio wave communication comprising a plurality ofmain conductors, each approximately one half a Wave length in height,and auxiliary conductors positioned at right angles to and connectingsaid main conductors in series, said main conductors being so spacedthatthe successive spacings are unequal and alternate conductors areseparated by a distance of approximately one wave length in thedirection of propagation of the communication Wave.

In witness whereof, I hereunto subscribe my name this 7th day of MarchA. D. 1927.

EDMOND BRUCE.

